Attach swords to mesh/skeleton for exporting as FBX
If you want the swords as part of the character mesh, you want to add sword bones that are children of each hand and use them to control the swords.


In the armature, add a bone for each sword, let's call them sword_l and sword_r. Position them where the sword handles are and have them as children of the hand bones. As children they will follow the hand bone but can be moved separately when desired.
For each sword, remove the child of constraint, and create a vertex group matching the bone name, sword_l for swordL and sword_r for swordR. In edit mode select all vertices and assign them a weight of 1.0 to the vertex group. This will make the entire sword move with the bone.





In object mode select both swords and the character and press &#9096; CtrlJ to join them into one mesh. The vertex groups from the swords will also be part of the combined mesh and each sword will now move with the sword bone. As the sword bones are a child of each hand bone, they will follow the hand movements unless you keyframe their location away from the hand.


This is your model with both sword bones.